Molecular imprinting of small particles, and production of small particles from solid state reactants

ABSTRACT

Small particles of polymeric material are produced by expansion of a mixture of monomers and a propellant. The size and shape of the particles can be precisely tailored by materials selection and expansion conditions. Particles of 10 nanometers to 100 microns can be produced. If monomers exhibiting solid state reactivity are utilized, the particles thus formed can be polymerized at any time after formation. The particles produced by this method can be molecularly imprinted by incorporating a template into the particle prior to fully curing the particle, in a manner which allows selective extraction of the template from the cured particle after formation without deformation of the imprint site. A two step polymerization process allows the particles to be deposited on and adhered to a wide variety of substrates without additional agents. The molecularly imprinted particles can be used in a wide variety of applications including the selective binding of analyte from a sample, where the analyte is the same as the template or is of substantially the same size and has a similar arrangement of chemical functional groups. Imprinted molecularly imprinted particles can be used for targeted delivery of agents in biological applications. Non-imprinted particles formed by the expansion technique using monomers of solid state reactivity can be used in optical data storage systems.

RELATED APPLICATION

This application is a divisional of application Ser. No. 10/054,708,filed Jan. 24, 2002 now U.S. Pat. No. 6,660,176 which is allowed and isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention pertains to molecular imprinting of small particles and,more particularly, to a method of molecular imprinting which utilizes apropellant as the solvent and dispersing agent of the matrix materialand to imprinted particles formed by the method as well as devicescoated with imprinted particles, such as, for example, surface acousticwave (SAW) devices. In addition, the invention pertains to a method forthe formation of small particles of monomers containing solid-statereactivity.

2. Description of the Prior Art

Molecular imprinting is a process, which involves arranging ofpolymerizable functional monomers around a template (print) molecule.This is achieved either by utilizing non-covalent interactions such ashydrogen bonds, ion-pair interactions, etc. (non-covalent imprinting),or by reversible covalent interactions (covalent imprinting) between theprint molecule and the functional monomers. Typically, a molecule to beimprinted (template) is combined with a mixture of functionalized andnon-functionalized monomers so that the monomers surround the template.In the process, functionalized monomers align themselves in a bindingrelationship to complementary functional groups on the template to formtherefore a complex with the template. After polymerization, functionalgroups are held in position by the highly cross-linked polymeric matrix.The template is then removed, and the resulting material containsimprinted binding sites which are complimentary in size and shape to thetemplate. The complementary binding groups, arising from thefunctionalized polymer groups incorporated during the imprinting, arespecifically positioned to enhance the preferential substrate bindingand, if desired, subsequent catalysis. The imprinted polymer materialsare capable of specific sorption or specific catalytic activity. A gooddescription of state of the art of molecular imprinting can be found inMosbach, K., Trends in Biochemical Sciences, Vol. 7, pp. 92-96, 1994;Wulff, G., Trends in Biotechnology, Vol. 11, pp. 85-87, 1993; andAndersson, et al., Molecular Interactions in Bioseparations (Ngo. T. T.ed.), pp. 383-394.

The functionalized monomers usually used for molecular imprinting are:acrylic acids [Anderson, L.; Sellergren, B; Mosbach, K Tetrahedron Lett.1984, 25, p. 5211. Sellergren, B.; Lepisto, M.; Mosbach, K. J. Am. Chem.Soc. 1988, 110, p. 5853. Andersson, L. I.; Mosbach, K. J. Chromatogr.1990, 516, p. 313. Matsui, J.; Miyoshi, Y.; Takeuchi, T. Chem. Lett.1995, p. 1007.], vinylbenzoic acids [Andersson, L.; Sellergren, B.;Mosbach, K. Tetrahedron Lett. 1984, 25, p. 5211], acrylamino-sulfonicacids [Dunkin, 1. R.; Lenfeld, J.; Sherrington, D. C. Polymer 1993, 34,p. 77], amino-metacrylamides [Beach, J. V.; Shea, K. J. J. Am. Chem.Soc. 1994, 116, p. 379.], vinylpyridines [Ramstrom, O.; Andersson, L.I.; Mosbach, K. J. Org. Chem. 1993, 58, p. 7562. Kempe, M.; Fischer, L.;Mosbach, K. J. Mol. Recognit. 1993, 6, p. 25], vinyl imidozales [Kempe,M.; Fischer, L.; Mosbach, K. J. Mol. Recognit. 1993, Vol. 6, p. 25.Leonhardt, A.; Mosbach, K. React. Polym. 1987, 6, p. 285.], acrylamides[Yu, C.; Mosbach, K. J. Org. Chem. 1997, 62, p. 4057.], andvinyl-iminodiacetic acids [Dhal, P. K.; Arnold, F. 14. J. Am. Chem. Soc.1991, 113, p. 7417. Kempe, M.; Glad, M.; Mosbach, K. J. Mol. Recognit.1995, 8, p. 35.].

Prior to this invention, methods of molecular imprinting have achievedonly modest success in the enhancing polymer selectivity and catalyticactivity. The reason for this is, that in order to be effective in awide scale, imprinted materials must have binding/active sites to behomogeneous (in specificity and activity), be well formed (based onshape and reactivity), and be easily accessible by the reactantmolecules (access is affected by shape, size and polarity of thechannels leading to the catalytic site). The imprinted polymericmaterials created by prior art methodologies have sites that aregenerally not very accessible and not homogenous, as they often havedifferent binding affinities and/or reactivities. These problems mainlyarise from the method used for producing the imprinted polymerparticles.

A common method of molecular imprinting is referred to as solutionpolymerization. This method results in the formation of imprinted sitesthat are completely encased within the polymer. In order to enable anaccess to those sites, the polymer monolith must be subjected tomechanically grinding to produce particles that have exposed sites.Grinding produces irregularly shaped particles and typically only lessthan 50 percent (50%) of the ground polymer is recovered as useableparticles with size less than 25 μm. Irregular particles generally giveless efficient devices mainly because of the deformation of a largenumber of the binding sites. As a result, damage to the sites adverselyaffects their selectivity and activity. An alternative method toincrease accessibility to the imprinted sites is by the use of porogencompounds which are known to generate foam-like polymer structures whencombined with polymer forming materials. Porogens, which are typicallyinert solvents, are mixed with the polymerizable monomers during theimprinting process and are washed away after polymerization is complete.This creates large pores that allow access to the created binding sites.However, while the porogens are removed, some of the structuralintegrity of the polymer can be lost at the same time, leading to thedeformation of the sites and loss in specificity and activity.

Another alternative for molecular imprinting is by direct polymerizationof particles in liquid media. Surfactants are used to create molecularmicrostructures, such as micelles or reverse micelles. Then, inorganicor organic monomers are polymerized around those molecularmicrostructures at the surfactant-solvent interface to form polymerbeads, dispersed in the liquid media to prevent agglomeration. The sizeand shape of the formed beads highly depend on the chemistry of themixture and reaction conditions, such as temperature and stirring. Whenthe surfactant is removed, the remaining material has a size and shapecomplementary to the size and shape of the initial molecularmicrostructures. By controlling variables such as surfactant selectionand concentration, a variety of different microstructure shapes such asmicellar, cubic, tetragonal, lamellar, tubular and reverse micellar canbe formed. Consequently, monodisperse particles of a variety ofdifferent sizes and porous materials with a variety of different shapesof pores and channels can be created. Methods of making porous materialare described, for example, in the following patents each of which areincorporated herein by reference: U.S. Pat. No. 5,250,282 to Kresge etal; U.S. Pat. No. 5,304,363 to Beck et al; U.S. Pat. No. 5,321,102 toLoy et al; U.S. Pat. No. 5,538,710 to Guo et al; U.S. Pat. No. 5,622,684to Pennavaia et al; U.S. Pat. No. 5,750,085 to Yamada.

Molecular imprinting by direct polymerization of particles in liquidmedia is more advantageous, but still has limitations due to the liquidmedia needed to disperse particles to prevent particles agglomeration.Therefore, after polymerization, particles need to be separated from theliquid media for further use, which is not an easy task, especially forsmall particles. While in many applications, imprinted polymers shouldbe deposited on the special surfaces, such as in chemical and biologicalsensors, and in chromatography and filtration devices. Deposition of theimprinted polymer material and adherence on the surface remains a bigproblem.

U.S. Pat. No. 5,587,273 to Yan et al., which is herein incorporated byreference, describes a way of molecular imprinting of polymer filmdirectly on the surface of sensor. The invention describes molecularlyimprinted substrate and sensors employing the imprinted substrate fordetecting the presence or absence of analytes. One embodiment of theinvention comprises first forming a solution comprising a solvent and(a) a polymeric material capable of undergoing an addition reaction witha nitrene, (b) a crosslinking agent (c) a functionalizing monomer and(d) an imprinting molecule. A silicon wafer is then spin coated with thesolution. The solvent is evaporated to form a film on the silicon wafer.The film is exposed to an energy source to crosslink the substrate, andthe imprinting molecule is then extracted from the film. Describedmethod is an advance in deposition of imprinted polymers to the sensingsurfaces. But there is no solution disclosed in the literature forimprinting of polymer particles directly on the surfaces of devices.Prior researchers have focussed on the preparation of imprintedparticles, but not on attachment of the particles to the surfaces ofdevice, and it would be advantageous to have a methodology which alloweddirect attachment of imprinted particles to substrate surfaces.

Aerosol and vapor technology has been used for many industrial andmedicinal applications which utilize particles. An aerosol is atwo-phase system consisting of a gaseous continuous phase and adiscontinuous phase of individual particles. The individual particles inan aerosol can be solids or liquids (Swift, D. L. (1985), “Aerosolcharacterization and generation,” in Aerosols in Medicine Principles,Diagnosis and Therapy (Moren, F. et al. eds) 53-75). Supercriticalfluids have been used in the production of aerosols for precipitation offine solid particles. The phenomenon was first observed and documentedas early as 1879 and was described the precipitation of solids fromsupercritical fluids (Hannay, J. B. and Hogarth, J., On the Solubilityof Solids in Gases, Proc. Roy. Soc. London, 1879, A29, 324). The suddenreduction in pressure reduces the solvent power of the supercriticalfluid, causing precipitation of the solute as fine particles. Thisphenomenon has been exploited in many processes for producing fineparticles, using co-solvents (Sievers, et al. PCT Publication WO 9317665published Sep. 16, 1993, Donsi, G. and Reverchon, E. (1991),“Micronization by Means of Supercritical Fluids: Possibility ofApplication to Pharmaceutical Field,” Pharm. Acta Helv. 66:170-173),anti-solvents (Debenedetti, P. G., et al. (1993), “Application ofsupercritical fluids for the production of sustained delivery devices,”J. Controlled Release 24:27-44, PCT Publication WO 90/03782 of TheUpjohn Company for “Finely Divided Solid Crystalline Powders viaPrecipitation Into an Anti-Solvent”, Yeo, S-D, et al. (1993), “Formationof Microparticulate Protein Powders Using a Supercritical FluidAntisolvent,” Biotechnology and Bioengineering 41:341-346), as well aspure supercritical solvents (Mohamed, R. S., et al. (1988), “SolidsFormation After the Expansion of Supercritical Mixtures,” inSupercritical Fluid Science and Technology, Johnston, K. P. andPenninger, J. M. L., eds., Tom, J. W. and Debenedetti, P. B. (1991),“Particle Formation with Supercritical Fluids—a Review,” J. Aerosol.Sci. 22:555-584, Smith U.S. Pat. No. 4,582,731 for “Supercritical FluidMolecular Spray Film Deposition and Powder Formation,” issued Apr. 15,1986, and Smith U.S. Pat. No. 4,734,451 for “Supercritical FluidMolecular Spray Thin Films and Fine Powders). In the processesdescribed, fine aerosols comprising the desired substance are formed bymixing a nongaseous pressurized or/and supercritical fluid(s) with thedesired substance, which is present in a solution, dispersion,suspension, micellar system or emulsion. During rapid reduction of thepressure on composition the pressurized/supercritical fluids form a gasand a gas-borne dispersion of fine particles, liquid or solid.

There are many acronyms associated with those processes, including RESS,GAS or SAS, SEDS, ASES, and PGSS (Jennifer Jung, Michel Perrut Particledesign using supercritical fluids: Literature and patent survey Journalof Supercritical Fluids 20 (2001) 179-219). RESS refers to RapidExpansion of Supercritical Solutions. This process contemplatesdissolving the product in the fluid and rapidly depressurizing thissolution through a nozzle, causing an extremely rapid nucleation of theproduct into a highly dispersed material. GAS or SAS is Gas (orSupercritical fluid) Anti-Solvent, one specific implementation beingSEDS (Solution Enhanced Dispersion by Supercritical Fluids). The generalconcept contemplates decreasing the solvent power of a polar liquidsolvent in which the substrate is dissolved, by saturating it withcarbon dioxide in supercritical conditions, causing substrateprecipitation or re-crystallization. ASES is used when micro- ornano-particles are expected. The process contemplates pulverizing asolution of the substrate(s) in an organic solvent into a vessel sweptby a supercritical fluid. SEDS is a specific implementation of ASESwherein there is co-pulverizing of the substrate(s) solution and astream of supercritical carbon dioxide through nozzles. PGSS stands forParticles from Gas-Saturated Solutions (or Suspensions). The processincludes dissolving a supercritical fluid into a liquid substrate, or asolution of the substrate(s) in a solvent, or a suspension of thesubstrate(s) in a solvent followed by a rapid depressurization of thismixture through a nozzle causing the formation of solid particles orliquid droplets.

Development of microspheres/capsules, containing a load of neededingredient, is one of the most rapidly developing area in medicine, foodindustry, agrochemicals, cosmetics. Many efficient drugs have beenreformulated to allow control of delivery location and rate, the activesubstance being distributed directly to the target to enhance thetreatment efficiency and reduce the doses and related side effects. Someof the researchers classify particles/capsules smaller than 1 μm asnanoparticles and those larger than 1000 μm as macro-particles.Commercial particles/capsules typically have a diameter between 3 and800 μm and contain 10-90 wt. % of carrier material. A wide range ofmaterials have been embedded/encapsulated in microspheres/capsules,including adhesives, agrochemicals, live cells, active enzymes (W.Fischer, B. Muller, Patent EP 0 322 687, 17 Dec., 1988; P. Debenedetti,J. W. Tom, S. D. Yeo, G. B. Lim, Application of Supercritical Fluids forthe Production of Sustained Delivery Devices. Journal of ControlledRelease, 24, 1993, 27-44; L. Frederiksen, K. Anton, B. J. Barrat, P. VanHoogevest, H. Leuenberger. Proceedings of the 3rd InternationalSymposium on Supercritical Fluids; Tome 3; G. Brunner, M. Perrut (Eds.),ISBN 2-905-267-23-8, 17-19 October, Strasbourg, 1994, 235-240; M. Hanna,P. York, Patent WO 95/01221, 1994; M. Hanna, P. York, Patent WO96/00610, 1995; K. Mishima, S. Yamaguchi, H. Umemoto, Patent JP8-104830, 1996; P. Pallado, L. Benedetti, L. Callegaro, Patent WO96/29998, 1996; W. Majewski, M. Perrut, Patent FR 99.12005, 27September). Despite these advances, there are few materials whichinclude an active agent embedded or encapsulated in a carrier matrix (orotherwise associated with the matrix) which are specifically designedfor targeted delivery of the active agent to a particular site. It wouldbe advantageous for example, if a material were available where a drugor toxin were associated with a slow release matrix material, whereinthe material could be targeted for delivery to a tissue, organ or othersite of activity, and then have slow sustained release at the targetedsite. Prior to this invention, no such delivery material having each ofthese attributes existed.

There are several method of handling materials with solid statereactivity to develop small particles of reacted solid materials. Thereis a need to produce small particles which retain reactivity in thesolid state. Reprecipitation in liquid solvents is one of the techniquesused (Application: JP 92-238160 19920907 to Kasai; Oikawa H; Oshikiri T;Kasai H; Okada S; Tripathy SK; Nakanisbi H. Various types ofpolydiacetylene microcrystals fabricated by reprecipitation techniqueand some applications. POLYMERS FOR ADVANCED TECHNOLOGIES 2000, Vol 11,Iss 8-12, pp 783-790). The process is carried out by dissolving anorganic material in a solvent, adding poor solvent, followed bycrystallization or polymerization of the microcrystals to formparticles. Adding 4-BCMU in EtOH solvents to water dropwise andirradiating with high-pressure Hg lamp gave polydiacetylene particlesshowing avarage diameter 100-200 nm. The reprecipitation method is auseful technique to fabricate organic microcrystals such aspolydiacetylene (PDA), low-molecular-weight aromatic compounds, organicfunctional dyes that have features located in a mesoscopic phase betweena single molecule and bulk crystals, and organic microcrystals which areexpected to exhibit peculiar optical and electronic properties.

One known variation involves recrystallization in supercritical fluid bychange of temperature and addition of antisolvents (Kasai, Hitoshi;Okazaki, Susumu; Okada, Shuji; Oikawa, Hidetoshi; Adschiri, Tadafumi;Arai, Kunio; Nakanishi, Hachiro. Fabrication of organic microcrystals bysupercritical fluid crystallization method and their optical properties.MCLC S&T, Sect. B: Nonlinear Opt. (2000), 24(1-2), 83-88; Komai, Y;Kasai, H; Hirakoso, H; Hakuta, Y; Okada, S; Oikawa, H; Adschiri, T;Inomata, H; Arai, K; Nakanishi, H. Section 3: Thin Films—Size and FormControl of Titanylphthalocyanine Microcrystals by Supercritical FluidCrystallization Method. Molecular Crystals and Liquid Crystals, 1998,v.322, p. 167, 6 p). This method involves the use of solvents whichmakes the particles thus produced only accessible in or subject to thesolvent as an impurity. It would be advantageous to have particles andparticle producing methods where both agglomeration and solventimpurities are completely avoided.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved method offabricating molecularly imprinted polymeric particles which canselectively bind specific compounds or classes of compounds.

It is another object of the invention to provide polymeric particleswhich are molecularly imprinted, and which are capable of substantiallyimproved performance over prior art materials made by differentmethodologies.

It is yet another object of the invention to provide devices which areused for highly selective binding of molecules or classes of molecules,which are coated with molecularly imprinted polymeric materials, such asfor example SAW devices and other sensors, chromatography devices andfilters, and purification devices of all types (e.g., cigarette filters,water filters, etc.).

It is still another object of the invention to provide a new andimproved method of making micron and less than micron sized particlesfrom compounds that have solid-state reactivity, with or withoutmolecular imprinting.

According to the invention, particles are created from a mixture ofpropellant and desired substance which is present in the form ofsolution, dispersion, suspension, micellar system or emulsion; whichcomprises at least one polymerizable monomer. A “propellant” is acompressed gas or mixture under elevated pressure, where at least one ofthe components of the mixture may be a supercritical fluid, and, whileexpanded, propellant dispenses the contents of the mixture to formparticles. The term “particle” as used herein refers to both solidparticles and liquid droplets. As the mixture passes through a capillarynozzle or other orifice, the mixture undergoes fast expansion so as tocreate fine particles of the mixture, containing monomer, that arepreferably less than 100 microns in size, and most preferably less than50 microns in size. In one embodiment, the particles includepolymerizable monomers with or without cross-linking agents, and aninitiating species (e.g., activators which initiate polymerization orcross-linking (or both processes)). In another embodiment, the monomersthemselves exhibit solid-state reactivity, meaning that they change froma solid monomer to a solid polymer without a change of the materialphysical state. This second embodiment can be used to make particles ofsubstantially uniform, small size, which can be molecularly imprinted ornot be molecularly imprinted, and constitutes a new manner of handlingmaterials with solid state reactivity. These particles are advantageousin that they are not agglomerated, and do not require a solvent. Inaddition, they are stable for long periods of time (e.g., 1-10 years)and can be selectively polymerized at any desired time. The particlesformed from solid state reactivity monomers can have wide rangingapplications including in the formation of coatings on surfaces and inoptical data storage.

For molecular imprinting, in either embodiment, a template can becombined with the mixture either before expansion or after particleformation. A template is used for imprinting the polymeric material, andcan be any molecule which is selectively releasable from a polymerformed from the monomers in the particle. In many applications, it ispreferable that the template does not covalently bond to the polymerwhich is formed. However, in some applications, the template may bereleased by hydrolyzing bonds or changing the ionic attraction between atemplate molecule and the polymer matrix. In molecular imprinting, thetemplate needs to be extracted from the polymer particle afterpolymerization of the monomer or monomer mixture in the particle formedby expansion. The template can be a chemical or biological compound orsubstrate (a portion of a biological or chemical compound, or abiological entity). The choice of template will depend on theapplication planned for the molecularly imprinted polymer particle.Specifically, the template may be a compound (e.g., toxin, carcinogen,or any compound of interest, etc.) that one would like to sense in agaseous or fluid environment, or a compound which is to be removed froma gaseous or fluid environment by selective binding to the molecularimprint site such as by a filter or other separation device. Theinvention may also have application in biology or biotechnology. In somecases antigens or enzymes of interest could serve as the templatemolecule, and then the imprinted polymer particles would be able toselectively bind the specific biological entities. Otherwise, themolecular imprinting can produce the artificial enzymes and antibodies.

However, it should be understood that the imprint can be designed toselectively bind, sorb, or otherwise associate with more than a singlecompound, which served as the template compound. Specifically, theimprinting process may allow the molecularly imprinted polymer particleto bind any molecule that has a size (spatial size) and/or arrangementof chemical functional groups which is substantially the same as saidtemplate. This should be especially useful in the preparation ofimprinted polymer particles that may be used, for example, in detectionor sorption of chemical and biological warfare agents. Specifically,compounds, which have a size and arrangement of chemical functionalgroups that are similar to nerve gas agents, or other chemical weapons,but which are not themselves potent substances, may be used tomolecularly imprint polymer materials that can then be used to bind,sorb or otherwise associate with the dangerous substances. In this way,the molecularly imprinted materials might be fabricated in a mannerwhich would be more safe than working with the dangerous substancesthemselves.

If the template is added to the mixture prior to expansion, thedistribution of the imprinted sites within the polymer particles isvirtually assured. This is because the propellant will solubilize and/ordisperse both the matrix forming compounds (i.e. the monomers) and thetemplate to form a homogenous mixture, and after the expansion theparticles are formed that contain matrix compounds and template evenlydispersed therein.

If the template is added to the mixture after expansion, the templatemust be diffused into the particles. This can be done in either the gasor liquid phase using a suitable carrier. Even distribution of theimprinted sites on the surface of the polymer particles may be achievedusing this technique because particles are formed with substantiallyuniform surface representation. The imprinted sites are readilyaccessible, as the particles surfaces are exposed to the analyte.

The propellant in the mixture being expanded can be 20-99.99% by weightof the entire mixture to be expanded. The mixture, containing at leastone monomer, be they monomers having a solid state reactivity, or amixture of monomers, crosslinkers and initiators, can be 80-0.01% byweight of the entire mixture. If the template is added to the mixture tobe expanded, the template can comprise 1-30.00% by weight of themixture.

This is the first time it has been shown that propellant can beeffectively used as a solvent or distribution agent in the formation ofmolecular imprinting in micron and submicron sized particles. Inparticular, it is the first time that a propellant has been used fordevelopment of micron and submicron sized particles from materials withsolid state reactivity. The propellant is maintained in a fluid stateunder pressure, but, when pressure is relieved, it instantly transitionsto a gaseous state. This allows the propellant to be immediatelyseparated from the monomers that will ultimately form the polymerparticle not containing impurities due to the propellant. The propellantmay advantageously be a supercritical fluid or may include as at leastone component a supercritical fluid. The supercritical fluid cansolubilize the monomers in the mixture which is to be expanded, andthen, after expansion, will leave the particles thus formed as a gas.Examples of propellants which can be used in the practice of thisinvention include, but not limited to, chlorofluorocarbons (freons),hydrofluorocarbons, alkanes, alkenes, noble gases (e.g., helium andargon), nitrogen, sulfur hexafluoride, fluorocarbons, nitrous oxide,hydrogen, ammonia, carbon monoxide and carbon dioxide.

The ratio of the propellant and monomers in the mixture to be expandedcan be adjusted to achieve the formation of particles of varying sizes.Likewise, the nozzle opening can be adjusted to control particle size.The choice of system pressure and temperature can be experimentallyoptimized and depends on the type of materials to be expanded, monomers,and propellant. The propellant could also be a mixture of more than onematerial. For example, two different gases might be used, or asupercritical fluid and another compound might be used.

A particularly advantageous aspect of this invention is to produce themolecularly imprinted particles or simply the small particles formedfrom materials of solid-state reactivity. Particles formed by expansionof a mixture containing propellant and solid state reactivity monomerswill not agglomerate, and will be free of solvent, and are stable forlong periods of time (1-10 years). These particles can be polymerizedinto solid particles without a change in the physical state of thematerial. Thus, these particles may deposited onto surfaces wheredesired (e.g., on sensors, optical devices), at a desired time, and beselectively polymerized at any time after formation of the particle.

A two step polymerization can be performed in one embodiment of thisinvention which is particularly advantageous for securing imprinted ornon-imprinted particles directly on the surface of a substrate. In thefirst step, a stream of particles emanating at the site of expansion issubjected to an energy source sufficient to cause an initialpolymerization of the monomer while particles are in flight towards adeposition surface or other collection location. This can be performedby radiant energy, such as ultraviolet, gamma radiation, infraredradiation, intense light in the visible spectrum, etc. Alternatively,heat can be used for specific monomers. The purpose of the initialpolymerization is to allow some of the polymerization or crosslinking tobegin. It is preferable that the initial polymerization is sufficient tomake the particles more viscous such that there physical morphologybegins to be established. The amount of energy applied will depend onthe materials in the composite particle containing monomers andtemplate, the size of the particle, whether or not initiators arepresent in the particle, the time of flight, and other factors. In thesecond step, the particles (which are now partially polymerizedparticles containing template material) are deposited onto a surface ofthe support, such as a SAW device, chromatography support, or filter,where they are subjected to more energy (e.g., heat or radiant energy)to fully polymerize the particle matrix directly on the surface of thesupport. This allows the particle to mechanically and/or chemicallyadhere to the surface of the support without having significant changesin its morphology of the particle. Specifically, the outer surface isfairly solidified in the initial polymerization, however, upondeposition onto a support, a portion of the particle containing monomerswould then be polymerizable in the final polymerization step. Thismonomeric portion may also be selected to chemically interact withfunctional groups on the support surface. Alternatively, the impact ontothe support surface will wedge some of the monomers into cavities anddepressions on the surface, whereupon the final polymerization step willassure a mechanical bond of the polymer particle within these cavitiesand depressions on the surface of the support. Thus, the polymericparticles of this invention are chemically or mechanically attached tothe substrate without using an adhering agent or requiring a separatestep to achieve good adherence. At the same time the method enablesuniform distribution of particles on the support surface.

Alternatively, the particles could simply be collected in a collectioncontainer and subjected to the energy sufficient to fully polymerize or“cure” the particles.

The procedure assures that the imprinted small particles ofsubstantially uniform size are formed. The invented procedures ofmolecular imprinting of polymer particles avoid deformation of theimprint sites by excluding grinding and solvent separation, enablesuniform distribution of the imprinted sites, and increases theiraccessibility to analyte. After formation of the polymeric particles,the template compound is extracted by exposing the polymer particles toexcess propellant/other supercritical fluid, or by any other meanssuitable for displacing the template from the polymeric particle.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects and advantages will be betterunderstood from the following detailed description of the preferredembodiments of the invention with reference to the drawings, in which:

FIG. 1 is a schematic view of an apparatus used for making micron andsub-micron particles, and which is the preferred apparatus configurationfor making molecularly imprinted particles according to this invention;

FIG. 2 is a graph showing the change in sensitivity of DSP polymer toalkanes after imprinting by heptane;

FIG. 3 is a graph showing the change in sensitivity of EPA polymer toalkanes after imprinting by heptane;

FIG. 4 is a schematic diagram of a system for depositing thin coatingsof articles on substrates which employs a movable stage; and

FIG. 5 is a schematic diagram showing the relationship of the nozzle inFIG. 4 the substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

With reference to FIG. 1, in the practice of this invention, a mixture10 containing at least one monomer and propellant is prepared. Thismixture 10 can be prepared in a tank 12 or other storage device, or canbe simply the intersection of a plurality of feed lines (not shown) formonomer, propellant, and template.

The “monomers” which can be used in the practice of this invention, arewide ranging. In one type of mixture, the monomers can include a mixtureof one or more of the following: functional monomers, cross-linkingagents, and initiators which initiate polymerization (e.g.,photoinitiators). Examples of functional monomers include acrylic acids,acrylamides, vinylbenzoic acids, acrylamino-sulfonic acids,amino-metacrylamides, vinylpyridines, vinylimidazoles,vinyl-iminodiacetic acids, etc. The monomers that can be used in thepractice of this invention can be of the variety that undergopolymerization reaction by any known mechanism, such as, cross-linking,polycondensation, or additive polymerization, as well as combination ofabove.

A wide variety of different crosslinkers may be used in the practice ofthis invention, including, but not limited to, ethylene glycoldimethacrylate (radical initiation), trimethylolpropane trimethacrylate(radical initiation), divinylbenzene (radical initiation), silane basedcrosslinkers (initiated by water), etc.

Initiators or other agents, which initiate polymerization and can beused in the practice are also wide ranging. In many applications, aphoto-initiator will be advantageously employed. For example, light, UVenergy, or some other source of radiant energy can be used toselectively activate the photo-initiator, which will then causepolymerization of the monomers to occur.

In one embodiment of this invention, monomers with a reactivity in thesolid state are used to prepare small particles of less than 100microns, and most preferably particles of a uniform small size less than50 microns in diameter (in some applications particles having diametersranging from 10 nm to 1 micron in size can be prepared). The solid statereactivity of specific organic and inorganic molecules has been knownsince 1916. Reactant materials of solid state reactivity, includingsolid state polymerization, can be low and high molecular weightsubstances (polymers, oligomers, monomers) with different physicalproperties. One embodiment of this invention involves small particlesfrom materials exhibiting solid state reactivity that can then undergosolid state chemical reaction in order to form materials with desiredproperties, including those with properties different from the bulkmaterial due to size reduction. Recently, small particles/microcrystalsfrom materials with solid state reactivity have attracted much ofattention due to the possible unique changes of properties due to thematerial size reduction. Examples of materials with known solid statereactivity include vinyl stearate (reaction initiated by gamma ray orelectron beam), vinyl acetate (reaction initiated by gamma ray),isoprene (reaction initiated by gamma ray), vinyl octacecyl ether(reaction initiated by gamma ray), methacrylic acid (reaction initiatedby ultraviolet (UV) or gamma radiation), trioxane (reaction initiated byring opening of BF₃(C₂H₅)₂O), diacetylenes (reaction initiated by heator UV light), and diolefinic compounds, containing two double bonds,such as, 2,5-distrylpyrazine (DSP) (reaction initiated by UV, gammarays, and visible light), 2,2′-(2,2-p-phenylene-divinyl)-bis-pyridine(reaction initiated by UV light), diethyl p-phenylenediacrylate(reaction initiated by UV light), dimethyl p-phenylenediacrylate(reaction initiated by UV light). The common formula of diacetylenes isas follows:

Common FormulaR—C≡C—C≡C—RWhere the examples of R can be:

The common formula of diolefinic compounds is:

where,A—is an atom or chemical groupB—is an atom or chemical groupX—is a chemical group.

An important feature of this invention is that fine aerosols comprisingthe desired substance are formed by mixing a propellant with the desiredsubstance, which can be present in a different state, such as, asolution, dispersion, suspension, micellar system or emulsion. Thepropellant may contain co-solvent, surfactants, antisolvents, and otherchemical constituents. In a preferred embodiment, the propellant mayinclude, for example, chlorofluorocarbons (freons), hydrofluorocarbons,alkanes, alkenes, noble gases (e.g., helium and argon), hydrogen,fluorocarbons, nitrous oxide, ammonia, carbon monoxide and carbondioxide. At least one of the components of the propellant can besupercritical fluid. Supercritical fluids are generally gases atatmospheric pressure, but above their critical pressure and temperatureassume a liquid-like density and solvent power, combined with theadvantages of gas-like viscosity and compressibility. During rapidreduction of the pressure on mixture 10 by discharge through a nozzle ororifice 14 into a chamber 16, at least one of the components of thepropellant forms a gas and a gas-borne dispersion of fine particles fromthe desired mixture (a particle flow 18) is discharged in chamber 16.The formed particles can be both liquid or solid. The chief requirementis that a uniform distribution of monomers and, template if included, isachieved with the propellant, and upon discharge through a nozzle 14,the propellant leaves its association in the mixture in a gas form toproduce a particle flow 18 in chamber 16. The propellant can be ventedfrom the chamber 16, or, it can be captured and recycled from thechamber 16 to the tank 12 using a pump.

An important feature of this invention is that monomers can besolubilized in propellant to make mixtures capable of expansion bydischarge through a nozzle or orifice 14 into a chamber 16. In this way,the propellant is used to make a mixture 10 that can be segregated intomany particles that are emanating from the nozzle or orifice 14. Thepropellant may contain co-solvent, surfactants, antisolvents, and otherchemical constituents. In a preferred embodiment, the propellant mayinclude, for example, chlorofluorocarbons (freons), hydrofluorocarbons,alkanes, alkenes, noble gases (e.g., helium and argon), hydrogen,fluorocarbons, nitrous oxide, ammonia, carbon monoxide and carbondioxide. Supercritical fluids are generally gases at atmosphericpressure, but above their critical pressure and temperature assume aliquid-like density and solvent power, combined with the advantages ofgas-like viscosity and compressibility. The propellant in this inventioncould contain at least one supercritical fluid, alone or in combinationwith a gas or other liquid. In addition, the propellant could includeother materials, which will solubilize monomers used in the practice ofthis invention. The chief requirement is that a uniform distribution ofmonomers and, template, if included, is achieved with the propellant,and upon discharge through a nozzle 14, the propellant leaves itsassociation in the mixture in a gas form to produce a particle flow 18in chamber 16. Specifically, as the mixture 10 is expanded through thenozzle due to entry of the mixture into a lower pressure environment,all of the gaseous components immediately leave the mixture, leavingonly the non-gaseous matrix forming components in the form of smallparticles. The propellant can be vented from the chamber 16, or, it canbe captured and recycled from the chamber 16 to the tank 12 using apump. This technique of particle formation, particularly, whensupercritical fluids are utilized in the propellant, is based on thetremendous solubility change that occurs during the sudden decompressionof a supercritical solution containing a nonvolatile solute by means ofan expansion device, such as an orifice or capillary nozzle. The highsupersaturation during fluid expansion results in the nucleation andgrowth of solute particles with mean size ranging from nanometers totens of microns. The size and morphology of precipitates is controlledby tuning the supercritical solution parameters (concentration ofsolute, pre-expansion temperature and pressure) as well as the geometryof the expansion device.

The propellant may comprise 20-99.99% by weight of the mixture, and themonomers and other constituents may comprise 80-0.01% by weight of themixture. In applications of this invention, the template molecule can beadded to the mixture 10 in tank 12, or can be added to the chamber 14for diffusion into the particle flow 16. If added to the mixture 10, thetemplate molecule can comprise 1-30% by weight of the mixture. The sizeof the particles in the particle flow can be controlled by adjusting theratio of propellant in the mixture, by choice of nozzle or orifice 14,and by the choice of monomers used in the matrix. The choice of systempressure and temperature are experimentally optimized and depends on thetype of materials to be expanded, monomers, and propellant. In certainapplications of this invention, particles smaller than 1 micron in size,which are imprinted with a template, can be produced.

In molecular imprinting, the template can be a chemical or biologicalcompound or substrate (a portion of a biological or chemical compound,or a biological entity).

Chemical compounds having a molecular weight ranging from 10 to1,000,000 can be used in the practice of this invention. The choice ofchemical compounds is wide ranging and can include, carbohydrates,halogenated compounds, alcohols, ethers, esters, amines, aldehydes,ketones, carboxylic acids, amides, oligosaccharides, polysaccharides,antigens, transition state analog (chemically stable compound andstructurally is very similar to the transition state formed during anenzymatic conversion of compound being catalyzed) steroids, nucleotides,nucleosides, oligonucleotides, polyanions, drugs, toxic industrialmaterials, chemical warfare agents, or chemical agent simulants,insecticides, pesticides, and fungicides. The template can be selectedfrom drugs such as antioxidants, chemotherapeutic agents, steroids,hormones, antibiotics, antiviral agents, antifungals, antiproliferativeagents, and antihistamines. Examples of proteins which could be used astemplates include nutrient protein, a storage protein, a contractile ormotile protein, a structural protein, a defense protein, regulatoryproteins (e.g., enzymes). Examples of chemical warfare agents which mayact as templates include nerve agents, such as Sarin (GB), Soman (GD),Tabun (GA), GF, TGD, VX; blister agents, such as mustard (HD), lewisite(L), HN-1, HN-2, and HN-3; and agent mixtures, such as HL and HT.Examples of chemical agent simulants which may be used as templatesinclude methyl salicylate, dimethyl methyl-phosphonate, and diethylmalonate, diphenyl chlorophosphate, 2-chlorethyl phenylsulfide, andO-ethyl-S-ethyl phenylphosphonothioate. Examples of substrates which maybe used as a template in the practice of this invention include cells(living or nonliving), DNA, proteins, enzymes, viruses, bacteria,nucleic acids, peptides, vitamins, drugs, pollen, and mold.

The template used for molecular imprinting will often be the analytethat is intended to be bound by imprinted polymer. For example, inpreparing a chromatography device or filter, the molecularly imprintedpolymeric particles of this invention might be intended to bind aparticular enzyme or insecticide in a solution under test (i.e., theenzyme or insecticide is the analyte in the chromatographic separationor filtration). In these cases, the template used to prepare themolecularly imprinted polymeric particles often will be the enzyme orinsecticide. However, in some situations, it will be advantageous tohave the template and analyte be different from one another. This allowsusing more useful or less hazardous templates instead of uncomfortableones to prepare a molecularly imprinted polymer sensitive to, forexample, a hazardous analyte. In this situation, there is a need to havea similarity between the template and analyte in molecular structure,such as geometric size and shape and/or location functional groups. Thisis described in U.S. Pat. No. 5,801,221 to Tanaka, which is hereinincorporated by reference, where it is explained that a template is thetarget molecule or a structural analog of the target molecule. Examplescan be found in the scientific literature, describing cases where ananalyte, different from the template, exhibited greater affinity to thetemplate-imprinted polymer [Dickert F. L. et al, Molecularly imprintedsensor layers for the detection of polycyclic aromatic hydrocarbons inwater, Anal. Chem. 1999, 71 (20), 4559-4563]. This was believed to bedue to the changes of cavities followed by the removal of the template.We show in the Examples below that heptane-imprinted DSP and EPApolymers exhibited higher affinity to the smaller in size molecules,such as hexane and pentane, as well as to the template molecule—heptane.This same concept can be extended to more hazardous materials asdescribed above.

The configuration shown in FIG. 1 is designed to provide sufficientenergy for an initial polymerization of the particles in the particleflow 18. During this stage, the monomers begin to polymerize and theparticles become more viscous. This can be accomplished by having theparticles pass through a region where they are exposed to an energysource sufficient to initiate polymerization. FIG. 1 shows this as UVregion 20, however, it should be understood that other forms of radiantenergy could be applied in the top portion of the chamber 16, includinggamma radiation, electron beam, visible light, and X-rays. Furthermore,heat energy could be applied. The type of energy input for the initialpolymerization will depend on the monomer materials being polymerized.Finally, a second polymerization, fully polymerizes or “cures” theparticles when they reach the collector 22. Examples of collectorsinclude flasks, tubes, filter surfaces, the surface of a SAW device,etc. Again, this second polymerization is accomplished using a source ofenergy such as heat or radiant energy. The chamber 16 could be filledwith air or an inert gas, such as nitrogen, but also could include onlythe propellant used in the mixture 10.

The two part polymerization process is especially useful when theparticles are to be adhered to the surface of a support, such as asensor or other device. In the initial polymerization, the particles are“formed” and partially solidified with the template in place. Thiscreates the particle with the template to be imprinted. The secondpolymerization affixes the particle to a device surface. This isaccomplished either by having functional groups of the monomers in theparticle chemically bond with functional groups on the support surface,and/or by having the monomers at the base of the particle which rests onthe substrate surface penetrate into depressions in the surface of thesupport, and polymerize therein to form a mechanical bond with thesubstrate. This method of particles polymerization on the surface ofdevice is a significant advance over other molecular imprintingtechniques.

First, the surface of a support is uniformly coated with particles, dueto the propellant-driven particle stream 18. Second, the molecularimprinting is not subject to distortion or deformation (i.e., theimprinted sites for bonding with analyte are undisturbed). Third, thereno additional bonding compounds are needed to affix the imprintedparticles to the surface (this avoids material changes to the particles,avoids extra steps in production of sensors and other devices, andavoids faults in the performance of devices due to the bonding compoundinterference with the real signal, detected upon bonding of analyte tothe imprinted particles). Another important advantage of the describedtechnique is the patterned deposition of imprinted polymer particlesover the surface of device, such as a biological or chemical sensor, bysimple use of a temporary mask covering specific areas to be leftuncoated. In this way, imprinted particles can be adhered only todesired surface areas.

The surfaces on which deposition of particles (which are molecularlyimprinted or not imprinted) can be a wide variety of materials. They maybe conductive, non-conductive, semiconductive (e.g., silicon or galliumarsenide), piezoelectric, magnetic or non-magnetic, quartz, glass,metal, polymer, ceramic, zinc oxide, lithium neobate, etc. In addition,the substrate could be porous or non-porous. For example, in a filter,the fibrils of the filter could be coated with molecularly imprintedpolymer particles such that a medium being filtered (e.g., water) couldpass through the fibrils, and analytes in the medium could bind at anynumber of molecularly imprinted particles.

After the particles are cured, the template is removed. This can beaccomplished by exposing the particles to excess propellant or otheragents which can displace the template from the site of imprinting inthe polymer particle. Supercritical fluid also can be used for templateextraction. If the template is bonded to the polymer by chemical bonds,ionic attraction, etc. the chemical bonds can be cleaved by any suitabletechnique (e.g., hydrolysis). In many applications, it will beadvantageous to use a template which does not form covalent bonds withthe monomers used to create the polymer particle. This makes extractionproceed by less disruptive measures such as simple displacement.

While FIG. 1 shows a system whereby polymerization occurs in two steps,it should be understood that polymerization can occur in a single-steppolymerization. For example, if molecularly imprinted particles aredesired, which are not to be attached to a substrate surface, one mightsimply polymerize the particles fully as they emerge from the nozzle 14and collect them in collector 22.

The preferred embodiment for molecular imprinting of particles can besummarized as a three step process set forth below:

Step 1

Form a mixture containing at least one monomer able to undergo thepolymerization or cross-linking and the propellant (20-99.99 wt %) underelevated pressure, at least exceeding atmospheric. The given mixture isthen subjected to fast expansion by lowering the pressure to result information of small particles in a size range of 10 nm-50 μm containingall the non-gaseous components of the mixture. Such expansion can beachieved by either the passage through the local narrow short orifice orlong capillary, or by fast changing the vessel volume.

An obligatory component for molecular imprinting is the introduction ofthe template to the particles. Template can be present initially as oneof the mixture components in this step 1 and therefore, is included inthe particle after the particles formation. Otherwise the template isadded after the particle formation by a diffusion of the template eitherfrom the gas or from the liquid phase.

In the case where the monomer has solid-state reactivity, the highlycrystalline monomer can go through an amorphous state due to the fastexpansion and/or due to the presence of other polymer componentspreventing crystallization. Then, there is a transition of the monomerfrom amorphous to a crystalline state during molecular imprinting. Thetransition from the amorphous to the crystalline state can be achievedby the exposure to the chemical or by temperature change.

Step 2

Polymerize at least the monomer part of the particle composition by anysuitable methodology (e.g., polymerization, cross-linking, orpolycondensation) in the presence of the template without a physicaldistortion of the particle morphology.

Step 3

Remove the template from the particles by the evaporation, dissolving,or extraction without a distortion of particle morphologies. Thetemplate can be evaporated from the particles by purging with inert gashaving smaller molecules than the template molecule over the particles.Removal of the template also can be achieved by exposing imprintedparticles to a liquid, subcritical or supercritical solvent thatselectively extract only the template with or without additional heat.

As discussed above, the particles produced by the molecular imprintingmethod show higher affinity to an analyte which is the same or similarto the template in size and structure (configuration of functionalgroups) than those particles of similar composition without theintroduction of template. Examples 1 and 2 show the preparation ofmolecularly imprinted DSP and EPA particles according to this invention.These examples demonstrate that the molecularly imprinted particles areselective for analytes of interest, and can be used as to separate,filter, analyze, purify, or otherwise act on an analyte of interest.Furthermore, as discussed above, Examples 1 and 2 demonstrate that thetemplate can be used to produce particles which selectively bindanalytes which are not identical (note the selectivity for n-hexane whenn-heptane was used as the template). What is required, is to have size(spatial size) and/or structural similarity (note that DSP and EPAparticles molecularly imprinted with n-heptane were not selective foriso-octane—while iso-octane has the same number of carbon atoms, but isnot of the same spatial size and it does not have a similar structure ofchemical functional groups).

This invention also has application in making very thin, patterned orunpatterned coatings on substrate surfaces. The methods used in Examples1, 2 and 5 illustrate methodologies whereby uniform thickness coatingsof molecularly imprinted particles can be obtained on a surfaces ofdifferent supports of interest. FIG. 4 is a schematic drawing of anapparatus used to deposit particles on a substrate surface. A movablestage 28 has a substrate 30 positioned thereon. The coating apparatus32, which is substantially as described in conjunction with FIG. 1, hasa nozzle 34 directed at the movable stage 28. The combination of apropellant assisted coating process, as described in conjunction withFIG. 1, and a moving stage 28, allows for a unique way of controllingthe substrate to be coated in a well defined position relative to thenozzle 34 and the formation of precision thin coatings, including thincoatings which can be used on small parts (e.g., the process would allowthe creation of a semiconductor chip separation devices wherein achannel could be selectively coated with particles of interest,including those with molecular imprinting having specific selectivity toanalyte). Examples 1 and 2 clearly demonstrate compatibility ofdeveloped coatings with micro fabricated devices such as SAW devices,while the particle size is smaller than spacing between interdigitalelectrodes. Other microfabricated devices can be selected fromacoustical devices (thickness shear mode (TSM), surface acoustic wave(SAW), acoustic plate mode (APM), flexural plate-wave (FPW)), opticalsensing devices, such as surface plasmon resonance (SPR), capacitance,impedance measuring devices. The solute material can be a low or highmolecular weight material, used alone or in conjunction with othercomponents.

In the processes described in conjunction with Examples 1, 2, and 5 themovable stage was a rotating platform. Thin coatings of solute weredelivered to a SAW surface with very high precision and reproducibility.This was accomplished by adjusting the solute concentration to a lowlevel (in the case of Examples 1, 2, and 5, the solute concentration wasbelow 1 wt % monomer; however, it should be understood that controlmight be achieved with higher solute concentrations, such asconcentrations with below 10-30 wt % monomer), as well the adjustment ofoffset position (x) between 0.5-5.0 cm. The final morphology ofdeveloped coatings can also be different from those achieved by othercoating methodologies. It depends on the type of solute and propellant,solute molecular weight, composition of particles, as well as processingconditions. The rotatable platform allows for exact placement of thesubstrate relative to the spray jet. However, the movable stage 28 couldbe a conveyor or any other device which can bring the substrate 30 to aprecise location below the nozzle 34. Movement below the nozzle canoccur a single time or multiple times in repetition until a desiredthickness of deposited particles is achieved. The optimization is to bemade for type or solute to be delivered, propellant used, and support tobe coated. Other factors having impact on the process includepre-expansion pressure, pre-expansion temperature, nozzle innerdiameter, nozzle length, nozzle to substrate distance, offset positionof the substrate from the nozzle, and the speed of movement of the stage28. For the SAW devices with DSP and EPA imprinted particles describedin conjunction with Examples 1 and 2, the technique allowed forformation of very thin coatings, which were highly reproducible (lessthan 2-7% standard deviation under various test conditions).

The molecularly imprinted particles of the present invention can havemany different applications. For example, they may be incorporated intothe filter of a cigarette to selectively bind tar and other unhealthymaterials before they are delivered to the lungs of the smoker. Theycould be incorporated into or deposited on a filter which separates outundesired agents (in the case of, for example, water or airpurification), or which serves to collect analytes of interest from asolution under test (e.g., binding enzymes or other materials in a urineor blood sample for diagnosis purposes). The particles can be depositedon substrates such as tubes, flasks, chromatography devices, SAWdevices, semiconductor chips, filter media, etc., or they may beunattached to such devices. If the particles are unattached, they can becollected in a container which may be used for chromatography,filtration, purification, etc. The molecularly imprinted polymerparticles may be associated with an indicator and serve as a sensor forthe detection of the presence or absence of an analyte of interest(although in many sensor applications, the indicator would not need tobe present on the sensor). In addition, the imprinted polymer particlesmight also be used in drug delivery applications such as those describedin Example 3.

In addition, in the present invention, imprinted particles can be madeusing the same propellant based methodologies using compounds other thanmonomers. The “compounds” can be polymers, proteins, mixture ofpolymers, mixture of proteins, or combination. For example, there is newconcept of molecular imprinting of Nylon-6 polymer with L-glutaminetemplate in the solution. The recognition of amino acids by L-glutamineimprinted-polymer was evaluated by binding experiments for L-glutamineand its analogues and it was revealed that the recognition was effectivefor L-glutamine by the imprinted polymer as compared with its racemateD-glutamine and L- or D-glutamic acid (Reddy, P. S., T. Kobayashi, etal. (2002). Molecular imprinted Nylon-6 as a recognition material ofamino acids. European Polymer Journal, 38(3): 521-529). The recognitionexperiments were extended to membrane filtration and quartz-crystalmicrobalance response by using the imprinted Nylon-6. Evidence was alsopresented by FT-IR analysis that the amide hydrogen-bonding interactionbetween the imprinted Nylon-6 and template was originated for the aminoacid recognition (Reddy, P. S., T. Kobayashi, et al. (1999). Molecularimprinting in hydrogen bonding networks of polyamide nylon forrecognition of amino acids. Chemistry Letters, (4): 293-294). 30. Whilemuch of the above discussion has been devoted to employing thepropellant assisted method for molecular imprinting of particles, itshould be understood that this method, due to its use of a propellant,has several new and advantageous applications for forming particles ofsolid state reactivity which are not molecularly imprinted. An importantadvantage of the particle formation methodology noted above, wherein amonomers of solid state reactivity are expanded into particles oftunable size and shape, is that the particles can be activatedimmediately or after collection, or at a later time up to 1-10 years andlonger. That is, the particles thus produced, whether they contain onlysolid state reactivity monomers or a mixture of such monomers with othermaterials, will hold their particulate shape until such time as finalpolymerization is induced. The particles can be nanoscale, or up to 100microns in size (for example, 10 nm-100 nm; 10 nm-1 micron; 1-10microns, etc., are all possible size dimensions of particles formed bythe above described methods). As discussed above, the particles formedaccording to the above processes can be used to uniformly coat thesurfaces of various substrates. They can be adhered to a substratesurfaces (e.g., quartz, glass, ceramic, metal, silicon, galliumarsenide, piezoelectric, polymer, etc.) without additional surfaceagents.

The embodiment for development of small particles with solid statereactivity can be demonstrated referring to the FIG. 1. An importantfeature of this invention is that monomers or any materials with solidstate reactivity can be solubilized in propellant to make mixturescapable of expansion by discharge through a nozzle or orifice 14 into achamber 16, which should be shielded from the energy source, needed toinitiate the reaction in the material. In this way, the propellant isused to make a mixture 10 that can be segregated into many smallparticles (less than 100 μm, and less than 1 μm for some applications)that are emanating from the nozzle or orifice 14. The propellant maycontain co-solvent, surfactants, antisolvents, and other chemicalconstituents. In a preferred embodiment, the propellant may include, forexample, chlorofluorocarbons (freons), hydrofluorocarbons, alkanes,alkenes, noble gases (e.g., helium and argon), hydrogen, fluorocarbons,nitrous oxide, ammonia, carbon monoxide and carbon dioxide.

The propellant in this invention could contain at least onesupercritical fluid, alone or in combination with a gas or other liquid.In addition, the propellant could include other materials, which willsolubilize monomers used in the practice of this invention. The chiefrequirement is that a uniform distribution of monomers and is achievedwith the propellant, and upon discharge through a nozzle 14, thepropellant leaves its association in the mixture in a gas form toproduce a particle flow 18 in chamber 16, which should be shielded fromthe energy source, needed to initiate the reaction in the material.Specifically, as the mixture 10 is expanded through the nozzle due toentry of the mixture into a lower pressure environment, all of thegaseous components immediately leave the mixture, leaving only thenon-gaseous matrix forming components in the form of small particles.The propellant can be vented from the chamber 16, or, it can be capturedand recycled from the chamber 16 to the tank 12 using a pump.

This technique of particle formation, particularly, when supercriticalfluids are utilized in the propellant, is based on the tremendoussolubility change that occurs during the sudden decompression of asupercritical solution containing a nonvolatile solute by means of anexpansion device, such as an orifice or capillary nozzle. The highsupersaturation during fluid expansion results in the nucleation andgrowth of solute particles with mean size ranging from nanometers totens of microns. The size and morphology of precipitates is controlledby tuning the supercritical solution parameters (concentration ofsolute, pre-expansion temperature and pressure) as well as the geometryof the expansion device. The propellant may comprise 20-99.99% by weightof the mixture, and the monomers and other constituents may comprise80-0.01% by weight of the mixture.

The particles developed by this technique also can be collected on thesurface of support, such as sensors, data storage media, semiconductors,electronic devices, films, filters.

The invented method of development of small particles, possessing solidstate reactivity has several advantages over the currently usedtechnique for handling materials with solid state reactivity. One of themost important advances is the ability to produce non-agglomerated smallparticles that retain solid state reactivity for a long period of time(e.g., up to 1 or 10 years). The monomer particles can be used alone orin combination with other materials, such as binders, polymers, ormixtures. The particles can be activated at any specific time. There isno impurities in particle composition due to the solvent residue.Particle size can be tailored by choosing experimental conditions, suchas concentration of the monomer, pre-expansion pressure and temperature,geometry of the expansion device. Particles can be developed with thesame as, or different from bulk monomer properties. (amorphous state ofthe highly crystalline DSP monomer; higher photoreactivity of the smallmonomer particles compared to the big crystals)

Example 4 describes a write-once read many times application (opticaldata storage method) which employs the particles formed by a mixture ofsolid state reactivity monomers and propellant. This embodiment of theinvention is based on preparing a composite material with requiredcomponents: small particles from a solid photosensitive monomerexhibiting solid state reactivity and polymer matrix; recordinginformation due to exposure to a light source; and developing the imageby thermal treatment (heating) optionally followed by finalillumination. A write-once read-many-times (WORM) data storage deviceutilizes small particles of a solid photosensitive monomer exhibitingsolid state reactivity that can undergo solid state polymerization underirradiation (by UV, visible, or IR light). Such recording materials havebeen described in the literature (Nakanishi, F.; Nakanishi H.; Kato, M.;Tawata, M.; Hattori, Shuzo. Dry-process recording material by use ofphotosensitized solid-state reaction of m-phenylenediacrilic acid. J.Appl. Polym. Sci. 1981, 26 (10) 3505-10).

In this application of the invention, a composition is preparedcomprising monomer particles that retain solid state reactivity that aredeposited into a polymer matrix. The monomers with the solid statereactivity is preferably selected from the group vinyl stearate, vinylacetate, isoprene, vinyl octacecyl ether, methacrylic acid, trioxane,diacetylenes, and diolefinic compounds, such as, 2,5-distrylpyrazine(DSP), 2,2′-(2,2-p-phenylene-divinyl)-bis-pyridine, diethylp-phenylenediacrylate dimethyl p-phenylenediacrylate. The polymer matrixpreferably is selected from the group of: polycarbonates, polysiloxanes,and polyesters (however, other polymer matrices may also be empolyed.Any techniques for monomer particles production can be used, includingone based on the use of fast expansion of propellant, orrecrystallization in the polymer matrix be evaporation of the solvent orchanging a temperature.

The polymer matrix is solidified to prevent dimensional changes in thefuture. The solidification of polymer matrix can be performed by curing,network formation, passing trough liquid-solid transition, evaporationof solvent. The composite material can be optionally passivated torelease any stress and prevent future matrix distortion. Then, theformed composite material is selectively exposed to energy sourcesufficient to polymerize monomer particles and to form a patternedimage. Any two-dimensional or three-dimensional image writing techniquecan be used. The writing technique selectively exposes only a portion ofthe monomer particles exhibiting solid state reactivity to radiantenergy. This causes polymerization of the exposed portion, withoutpolymerization of the unexposed portion.

After that, the composite material comprised of polymer particles,monomer particles, and polymer matrix is subjected to heat at atemperature and for period of time sufficient to cause monomer particles(which did not undergo a solid state reaction) to diffuse into polymermatrix (this is usually for less than 10 minutes, but the time can varydepending on the temperature, choice of materials, etc.). Then, theprepared material can optionally subjected to an energy source (finalillumination or heat treatment) for preferably a short period of time topolymerize diffused particles in the matrix, but away from the writtenimage. An advantage of the described method is that thick materials canbe prepared that are capable of optical data storage, such astwo-dimensional or three dimensional materials.

EXAMPLE 1

2,5-distrylpyrazine (DSP) is a monomer that does not need any externalphotoinitiator to activate a reaction of polymerization in the solidstate under UV-light irradiation. The apparatus we used had a stainlesssteel vessel with floating piston to keep the mole fraction of themixture constant and to maintain a constant pressure during theexpansion. The maximum working pressure and temperature of the apparatuswas 10,000 psi and 250° C., respectively. The expansion nozzle was afused silica capillary with the inner diameter of 100 μm and length of20 mm. The propellant used was chlorodifluoromethane (Freon-22). DSPmonomer 0.2 wt % was placed into the vessel first at room temperature.Then the vessel was closed and propellant was charged into the vessel.The vessel was heated to 120° C. and pressurized to 5000 psi. After twohours, the mixture was expanded trough the nozzle into the collectionchamber at the pre-expansion conditions: temperature 120° C., pressure5000 psi. The particles were collected directly onto Surface AcousticWave (SAW) transducers of 250 MHz resonant frequency.

Propellant gas was vented from the collection chamber. Then SAW withcoatings were exposed to heptane vapors for 10 minutes, and in presenceof heptane vapors irradiated by UV light for 15 minutes (using 100 WattUV lamp, PC-100S, American Ultraviolet Co, providing a spectral range of325-382 nm at 22 cm distance). After polymerization the particles wereflushed with dry nitrogen for 20 minutes to remove template.

A custom-built dynamic flow sensor calibration system was used toevaluate the imprinting effect. The system accommodates two isolated SAWdevices (SAW PRO-250 from Microsensor Systems, Inc.): one coatedresonator and one uncoated used as a reference device. The temperatureof both SAW devices was maintained at 30±0.5° C. Test vapors weregenerated by means of evaporation using fritted u-shaped spargers filledwith liquid analyte and controlled at 10±0.1° C. The flow rates wereregulated in a range of 0.1-0.5 L/m in order to control the analyteconcentration. Research grade nitrogen was used as a carrier gas anddilutant. The test gas was applied repeatedly to the sampling resonatorwith a typical duty cycle of 60 seconds followed by purging with drynitrogen, while the reference SAW resonator was exposed to a purenitrogen stream with a matching flow rate.

The response of SAW transducers coated with the imprinted DSP polymerparticles was compared to the response of the SAW device coated with theparticles of matching particle size and coating thickness. Analytes usedwere a family of alkanes with different size of molecular chain,including template, such as pentane, hexane, heptane, octane, nonane,and decane. FIG. 2 shows the change in selectivity of heptane imprintedDSP particles. It can be seen that for n-hexane and n-heptane, themolecularly imprinted polymer particles are significantly more selectivethan the non-imprinted devices. This selectively rapidly dissipates asthe analyte becomes larger (note the decrease for n-octane, n-nonane,and n-decane. Furthermore, FIG. 2 demonstrates that the structure of theanalyte plays an important role in selectivity. By comparing the resultsof iso-octane and n-octane, two compounds of the same carbon make up butof different structure and spatial size, it can be seen that the DSPmolecularly imprinted with heptane was not significantly more selectivefor isooctane than the non-imprinted DSP.

EXAMPLE 2

p-phenylenediacrylate (EPA) is a monomer capable of polymerization inthe solid state. The apparatus was the same as described in theExample 1. The expansion nozzle was a fused silica capillary with theinner diameter of 100 μm and length of 20 mm. The propellant used waschlorodifluoromethane (Freon-22). EPA monomer 0.07 wt % was placed intothe vessel first at room temperature. Then vessel was closed andpropellant was charged into the vessel. The vessel was heated to 120° C.and pressurized to 5000 psi. After two hours, the mixture was expandedthrough the nozzle into the collection chamber at the preexpansionconditions: temperature 130° C., pressure 5000 psi. The particles werecollected directly onto a SAW transducers of 250 MHz resonant frequency.Propellant gas was vented from the collection chamber. Then SAW withcoatings were exposed to heptane vapors for 10 minutes, and, in thepresence of heptane vapors irradiated by UV light for 15 minutes (using100 Watt UV lamp, PC-100S, American Ultraviolet Co, providing a spectralrange of 325-382 nm at 22 cm distance). After polymerization, theparticles were flushed with dry nitrogen for 20 minutes to removetemplate.

FIG. 3 shows the change in selectivity of heptane imprinted EPAparticles. It can be seen that for n-hexane and n-heptane, themolecularly imprinted polymer particles are significantly more selectivethan the non-imprinted devices. This selectively rapidly dissipates asthe analyte becomes larger (note the decrease for n-octane, n-nonane,and n-decane. Furthermore, FIG. 3 demonstrates that the structure of theanalyte plays an important role in selectivity. By comparing the resultsof iso-octane and n-octane, two compounds of the carbon make up but ofdifferent spatial size and structure, it can be seen that the EPAmolecularly imprinted with heptane was not significantly more selectivefor isooctane than the non-imprinted EPA.

EXAMPLE 3

Enzymes perform a key role in living organisms, catalyzing thetransformation of substrates to specific products. In general, enzymesare proteins (polypeptides) of varying size and amino acid residuecomposition. Each enzyme is designed to catalyze a specific reaction.The high reaction rate and the selectivity of the reaction are twocharacteristics of the enzyme-catalyzed reactions. The preparation ofmaterials possessing enzymatic behavior is useful to catalyze thereaction of industrial interest, especially in reactions for which nonatural enzyme is available. One of the key features of a naturalenzymatic process, apart from the high rate of reaction, is selectivity.The selectivity of enzymes is highlighted by the following:

-   -   1) Enzymes are able to direct the chemical reaction to one        specific part of the substrate, e.g. an enzyme may catalyze a        chemical reaction at one specific site on the substrate while        leaving other sites unaffected. These may be equally liable to        reaction when performing the reaction by chemical means.    -   2) Enzymes are selective for their substrates. Enzymes can        operate in a mixture of compounds, but bind and act upon only        one (the substrate) or a few of the components of the mixture.    -   3) Enzymes are selective with respect to the chemical reaction        performed. One substrate may undergo a variety of chemical        conversions, each catalyzed by a specific enzyme.    -   4) Enzymes can perform their chemical reactions selectively with        respect to the stereostructure of the substrate and product.        Only one enantiomeric form of a substrate can be converted or        from a prochiral substrate (i.e., only one enantiomeric form of        the product is produced).        All of these types of selectivity of enzyme catalysis are        attractive for the chemist to mimic in the construction of        synthetic enzymes by molecular imprinting technique. In contrast        to the enzymes, antibodies are capable to bind selectively to        antigens. The formed antibody-antigen complex, is also a        subjected of further conversions. The preparation of synthetic        enzymes is well recognized and includes the synthesis of        compounds based on natural starting material (cyclodextrin) (R.        Breslow, A. W. Czarnik, J. Am. Chem. Soc. 105, 1390 (1983)) and        the preparation of fully synthetic systems (J-M. Lehn, C.        Sirlin, J. Chem. Soc. Chem. Commun., 949, (1978) and D. J.        Cram, P. Y. Lam, S. P. Ho, J. Am. Chem. Soc, 108, 839 (1986)).        U.S. patents describing molecular imprinting used for        development of artificial enzymes are U.S. Pat. No. 5,110,833        Mosbach and U.S. Pat. No. 5,801,221, Tanaka, et al., each of        which have been incorporated herein by reference.

While not previously recognized, imprinting of nanoparticles can be veryuseful for drug targeting as well. Nanoparticles are solid, colloidalparticles consisting of macromolecular substances that vary in size from10 nanometers (nm) to 1000 nm. In this embodiment of the invention, thedrug is dissolved, entrapped, adsorbed, attached, or encapsulated in themacromolecular material(s). Choosing the appropriate polymer, particlesize, and method of production would depend on three major aspects:bioacceptability of the polymer, physicochemical properties of the drug,and the type of therapy the drug should have. The use of polymers fornanoparticles is usually restricted by their bioacceptability. Thebioacceptability is affected by the polymer and the supplementarycomponents, as well as by particle size (Microparticulate systems forthe delivery of proteins and vaccines. Ed. S. Cohen, H. Bernstein, 1996,Drugs and Pharmaceutical Sciences, 77). A reduction in the particle sizeof the polymeric particles has many advantages, which are listed below.

1.) Intravenous injection can be allowed if there is a decrease in theparticle size.

2.) Intramuscular and subcutaneous distribution require small particlesize.

3.) Irritant reactions at the injection site are minimized by usingsmall particle size.

4.) Carcinogenic effects depend on particle size.

Some important practices for which nanoparticles are used include theadsorbing and coating of organs and tissues, peroral administration ofdrugs, vaccinations, the delivery of anti-inflammatory drugs, and thedelivery of drugs for diseases and tumors. Significant efforts in thisfield are now focused on the surface modifications of thenanoparticulate drug carriers in order to improve their targetingproperties. Therefore molecular imprinting of drug carriers can improvethe interactions with specific epithelial cells to target specificsites. This invention, therefore, particularly contemplates amolecularly imprinted particle with an active agent (e.g., drug in thecase of a therapeutic agent; toxin or oxidizing agent in the case of acancer treatment, etc.) associated with the particle. The particle wouldbe imprinted with a target molecule (e.g., enzyme, etc.) or substrate(cell, DNA, RNA, etc.) which would allow the particle to bind to thebiological material of interest, and would then deliver the active agentat the targeted site. This can occur by dissolution of the polymerparticle with subsequent release of the active agent, or by the activeagent present on the surface of the polymer particle being free to takeits intended action, or by other means. In contrast to the enzymes,antibodies are capable to bind selectively to antigens. According to thepresent invention, the synthetic antibody would be developed as theimprinted particle capable of the template specific binding, for exampleto specific antigen. While the particle (synthetic antibody) is bound tothe site of interest, it can stay at the site certain time. Theimprinted particle (synthetic antibody) may include otherchemical/biological compounds, which are not needed for molecularimprinting, but can be incorporated into the molecularly imprintedparticle. When such prepared “loaded” synthetic antibody binds to thetemplate specific site, the “load” can be released from the particle.The load to artificial antibodies can be selected from drug,neurotransmitters hormone, or the other biologically active compounds orcatalyst. Released load is administrated to the area of theantigen-antibody complex in order to make changes to the livingorganism. This can occur by dissolution of the polymer particle withsubsequent release of the active agent, or by the active agent presenton the surface of the polymer particle being free to take its intendedaction, or by other means.

EXAMPLE 4

This embodiment of the invention is based on preparing a compositematerial with required components: small particles from a solidphotosensitive monomer exhibiting solid state reactivity and polymermatrix; recording information due to exposure to a light source; anddeveloping the image by thermal treatment (heating) optionally followedby final illumination.

Step 1. Preparing a Composite Material

A write-once read-many-times (WORM) data storage device utilizes smallparticles of a solid photosensitive monomer exhibiting solid statereactivity that can undergo solid state polymerization under irradiation(by UV, visible, or IR light). Such recording materials have beendescribed in literature (Nakanishi, F.; Nakanishi H.; Kato, M.; Tawata,M.; Hattori, Shuzo. Dry-process recording material by use ofphotosensitized solid-state reaction of m-phenylenediacrilic acid. J.Appl. Polym. Sci. 1981, 26 (10) 3505-10). The small particles of themonomer are embedded in a polymer matrix and can diffuse into thepolymer matrix under heat treatment. The polymer for the matrix must betransparent to the light used as the writing source, thermostable, andmechanically stable (i.e. does not change dimensions after thermaltreatment and over time during storage).

Form a data storage media from the composition of a photosensitivemonomer possessing solid state reactivity and a polymer matrix by anysuitable technique (Examples include: injection molding, coatingtechniques etc.). Solidify the polymer matrix by curing, networkformation, or passing through liquid-solid transition. Optionallypassivate the resultant composite material to prevent furtherdimensional changes that can cause image distortion. Any technique formonomer particles production can be used. We used 2,5-distyrylpyrazine(DSP) 100 nm particles produced by the fast expansion of propellant, asdescribed in the present invention. Particularly, clorodifluoromethane(99.8 wt %) was used as a propellant. The mixture was expanded throughthe nozzle into the collection chamber at the pre-expansion conditions:temperature 120° C., pressure 5000 psi. The collected chamber was madeto prevent light from entering. The particles are collected on thesurface of support (glass microscope slides) to form a coatingconsisting from small particles. As an example of a polymer matrix weused polydimethylsiloxane methyldiacetoxy terminated (PDMSMA) CAS#70879-95-7. Polymer was cast over the coating of DSP particles and alayer from the DSP-PDMSMA mixture having thickness of 0.7 mm wasprepared in the dark environment. Then the polymer matrix was cured in adark environment by water vapor and the resultant composite material waspassivated at 40° C. for 30 minutes to prevent further dimensionalchanges that can cause image distortion.

For two-dimensional images sometimes the use of polymer matrix can beoptional. We developed a dry-process recording material from DSP 100 nmparticles without use of polymer matrix. The image was created accordingto the step 2, without need of polymer matrix curing. After imagedevelopment by short heating (step 3), the image is stable and ready forreadout of information. Thus, polymer matrix optionally can be avoidedfor some cases, for thin coatings for example.

Step 2. Recording the Information

Write the information to be stored (2-D or 3-D) by means of a lightsource device (laser, for example), that induces the solid statereaction in the monomer particles. We used, for example, UV laser with365 mm wavelength and 100 Watt UV lamp, providing a spectral range of325-382 nm. Where exposed, the DSP monomer particles undergo solid statepolymerization under irradiation by UV light, resulting in the formationof a high molecular weight polymer structure. We recordedtwo-dimensional images using physical mask to form a patterned image.One can understand that any known methods of recording of opticalinformation can be employed.

Step 3. Image Development

Generally, to prevent image smearing (damage) in the presence of anyfuture irradiation during data readout or storage an additionalstep—image development is needed. We introduced a short thermaltreatment as an image development technique.

We heated the data storage device consisting of DSP-PDMSMA compositelayer having thickness of 0.7 mm with recorded information to atemperature of 200° C. for 2-5 minutes. The unreacted DSP monomer,diffuses into the polymer matrix during heating, while reacted DSPpolymer developed during information recording does not. The differencein diffusion and vapor pressure between the reacted and unreactedmaterial provides the image preservation. The image is clearly seenafter that. After the development step the data storage device is stableand ready for readout of information. In some cases it may be necessaryto illuminate material to fix the unreacted particles in the polymermatrix away from the image.

This embodiment of the invention provided a method whereby a twodimensional or three dimensional image may be stored for later use. Thesolid photosensitive particles produced according to the describedtechnique need only be combined with a polymer matrix to preserve aspacious structure of the layer of particles. The image is then createdby a writing source such as laser light directed at the particles, whichcauses the imaged particles to polymerize, with a fast thermal treatmentto develop the image. That is, the difference between reacted particles(those exposed during radiation) and unreacted particles (those notexposed) in diffusing into the polymer matrix fully develops the image.Thus optical storage is obtained by a three step process whereby 1)particles are developed by the fast expansion of propellant and mixedwith/without polymer matrix, 2) a precise writing tool directs energy atthe coated polymer matrix to selectively form two dimensional or threedimensional structures by selectively polymerizing the monomer particlesthereon, and 3) developing by a simple heat treatment to fix the imageby a difference in diffusion properties between reacted and unreactedparticles. The described materials for storing optical data areadvantageous over the prior art as having greater physical thickness ofthe composite layer, up to 1 mm, and up to 5 mm in some cases with smallparticles. This is important for three dimensional images such asholography.

EXAMPLE 5

The methods used in Examples 1 and 2, and described above in conjunctionwith FIG. 4 illustrate methodologies whereby thin uniform thicknesscoatings are formed from low and high molecular weight substances,consisting of particulate morphologies or uniform films,chemically/mechanically adhered to the surfaces. Surfaces to be coatedcan be conductive, non-conductive, semiconductive (e.g., silicon orgallium arsenide), piezoelectric, magnetic or non-magnetic, quartz,glass, metal, polymer, ceramic, zinc oxide, lithium neobate, etc. Inaddition, the substrate could be porous or non-porous.

FIG. 5 shows a schematic diagram of the nozzle region that pertains tothe system shown in FIG. 4. In FIG. 5, the moveable stage 28 holds oneor more substrates 30 a distance h below the nozzle 34. The offset xrepresents the distance the substrate 30 is positioned from directalignment with an outlet of the nozzle 34. The radius R represents theradius from the center of rotation to the center of the spray fromnozzle 34. In one experiment where polymer was deposited over a SAWdevice with 250 MHz resonant frequency, the copolymer 50%methylphenyl-50% diphenyl siloxane was deposited fromchlorodifluoromethane to result in coating thickness of 350 kHz atconditions as follow: solute concentration—0.11 wt %; offset (x)—1.0 cm;nozzle-to-substrate distance (h)—2.5 cm; rotation speed—4.12 rpm; radiusfrom the center of rotation to the imaginable center of the spray(R)—6.0 cm; pre-expansion temperature—125 C; pre-expansion pressure—5000psi. In another experiment pertaining to monomer deposition over the SAWdevices with 250 MHz resonant frequency, the 2,5-distyrylpyrazine (DSP)monomer was deposited from chlorodifluoromethane to result in coatingthickness of 90 kHz at conditions as follows: solute concentration—0.15wt %; offset (x)—0.8 cm; nozzle-to-substrate distance (h)—2.0 cm;rotation speed—5.23 rpm; radius from the center of rotation to theimaginable center of the spray (R)—6.0 cm; pre-expansion temperature—130C; pre-expansion pressure—5000 psi.

For the SAW devices with 250 MHz resonant frequency coated with monomerand polymer particles described in conjunction with Examples 1 and 2,the acoustical thickness, expressed as a frequency shift of 250 MHzresonant frequency device, can vary from 90 to 1,000 kHz.

The offset serves an important function in that it allows thin coatingsof solute (e.g., monomers, polymers, etc.) to be created withoutmicroscopic defects due to physical impaction of the stream on thesubstrate surface.

While the invention has been described in conjunction with its preferredembodiments, those of skill in the art will recognize that the inventioncan be practiced with considerable variation within the spirit and scopeof the appended claims.

1. Polymeric particles, which are molecularly imprinted, produced by aprocess comprising the steps of: expanding through a nozzle or anorifice a mixture containing a propellant in liquid form, monomers, anda template which does not covalently bond to said monomers to formparticles containing said monomers in the presence of said template andto release said propellant from said mixture in the form of a gas;polymerizing said monomers in said particles in the presence of saidtemplate to form composite particles having polymer and template,wherein said template is not covalently bound to said polymer; andextracting said template from said composite particles withoutdistorting a morphology of said composite particles to providepolymerized particles imprinted by said template with a size andarrangement of chemical functional groups complementary to said templatewherein said polymerized particles imprinted by said template are 1micron or less in size.
 2. The polymeric particles of claim 1 whereinsaid polymerizing step is performed by exposing said particles toradiant energy while said particles are in flight in a direction awayfrom said nozzle or orifice.
 3. The polymeric particles of claim 1wherein said template is selected from the group consisting of proteinsand nucleic acids.
 4. The polymeric particles of claim 1 wherein saidpolymer is selected from the group consisting of diolefinic compounds.